[concurrency-interest] JSR-133 Cookbook and exit monitor

√iktor Ҡlang viktor.klang at gmail.com
Wed Oct 8 08:30:37 EDT 2014


On Wed, Oct 8, 2014 at 2:09 PM, Remi Forax <forax at univ-mlv.fr> wrote:

>
> On 10/08/2014 12:51 PM, √iktor Ҡlang wrote:
>
> Sounds really bad if this is the case. I can totally understand eliding
> locks that are re-taken in a nested fashion, but coarsening in terms of
> coalescing neighboring acquisitions seems dubious.
>
>
> even in this case,
> class Foo {
>   public synchronized void setBar(Bar bar) { ... }
>   public synchronized void setBaz(Baz baz) { ... }
> }
> ...
>   Foo foo = ...
>   foo.setBar(bar);
>   foo.setBaz(baz);
>
> because sadly this code is very common :(
>

Agreed. The case above is not really problematic since there are no
invocations/reads/writes in between.


>
> Rémi
>
>
>
> On Wed, Oct 8, 2014 at 12:19 PM, thurstonn <thurston at nomagicsoftware.com>
> wrote:
>
>> Hello,
>>
>> If I read the  jsr-133 cookbook
>> <http://gee.cs.oswego.edu/dl/jmm/cookbook.html>   correctly, given the
>> following:
>>
>>
>> <code>
>> //y is a global, non-volatile
>> enter monitor x
>> ...
>> //do some work not involving y
>> . . .
>> exit monitor x
>> y = 43
>>
>> </code>
>>
>> then at least according to the JMM, the following execution is possible:
>> <code>
>> //y is a global, non-volatile
>> enter monitor x
>> ...
>> //do some work not involving y
>> y = 43
>> exit monitor x
>> </code>
>>
>> as in the first table in the cookbook, *normal stores* are allowed to be
>> re-ordered before a *monitor exit* (but not before a *monitor enter*).
>>
>> Although the issue isn't really one involving memory consistency, is that
>> really allowed?  Because *increasing* the size of a critical section
>> seems .
>> . . I don't know . . . unhealthy.
>> What if the program code computed the first 1000 prime numbers or
>> something
>> and wrote them to a global array (after the monitor exit)?
>>
>> I was always under the impression that only the operations specified
>> within
>> a critical section would actually be executed between the enter/exit
>> monitor
>> pair
>>
>> NB: Although, presumably the runtime/CPU would only do this if the
>> critical
>> section was leading to CPU stalls or the like and so in reality, not
>> really
>> producing a longer critical section execution time
>>
>>
>>
>>
>> --
>> View this message in context:
>> http://jsr166-concurrency.10961.n7.nabble.com/JSR-133-Cookbook-and-exit-monitor-tp11323.html
>> Sent from the JSR166 Concurrency mailing list archive at Nabble.com.
>> _______________________________________________
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>
>
>
> --
>  Cheers,
>>
>
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-- 
Cheers,
√
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